1. Field of the Invention
This invention relates to a blind fastener device, and also to a method of clamping a component to a support plate using a blind fastener device.
2. Description of the Related Art
It is of course well-known to provide anchor bolts for fixing to concrete, and in which an expanding sleeve is engaged by a conical head as the fixing is tightened, with the component parts of the sleeve moving radially outwardly into firm gripping engagement with the wall of the passage formed in the concrete to receive the fixing.
However, the invention is not primarily concerned with fixings of this type, (to anchor devices to concrete or brick work), but to the clamping of components to "rolled hollow metal sections" of the type being used increasingly as part of the supporting structure in current industrial building work. Support columns can be formed by square or rectangular box sections, built up from four metal rolled plate sections. When it is desired to secure fixing brackets, pipe supports, electrical conduits, (or any other components of the type used in an industrial building), to a hollow section, it is of course necessary to use "blind fasteners", since access cannot readily be obtained to the interior of the hollow section to complete the fastening operation. Therefore, using blind fasteners, an expanding sleeve is introduced through aligned openings in the section and the component to be clamped thereto, and a threaded portion is then rotated to draw a conical head into engagement with the inner end of the sleeve to expand the sleeve radially outwardly. The sleeve is usually slotted, so that it is composed of a number of axially extending portions forming separate "legs", each of which can be deformed outwardly by the conical head and thereby anchor the entire sleeve in the hollow section.
Conveniently, the conical head is temporarily attached to the inner end of the sleeve, so that the sleeve and conical head can be introduced as a single assembly through the opening in the hollow section, and then a threaded fastener can be taken through the component (to be clamped to the hollow section), pass through the head of the sleeve and into threaded engagement with an internal thread in the conical head, and further rotation of the threaded portion pulls the conical head into the inner end of the sleeve so as to expand the sleeve "legs" radially outwardly.
One known design of blind fastener for use with metal sections comprises a slotted sleeve, a conical head temporarily attached to the inner end of the sleeve e.g. by shearable connections, and a specially formed sleeve head at the opposite end of the sleeve to the conical head. The sleeve head comprises a gripping ring formed with a series of radially projecting teeth or other knurling, the purpose of which will be described below.
Evidently, once the sleeve has been introduced into the opening in the hollow section, and the threaded fastener e.g. a bolt is introduced into the sleeve, it is necessary to provide some means whereby rotation of the conical head is prevented so that the sleeve can be moved axially into the interior of the sleeve. In the known construction, in which the conical head is attached to the sleeve, the means for preventing rotation of the conical head comprises the specially formed sleeve head which is able to make gripping engagement with the wall of the opening in the hollow section. This works generally satisfactorily, but evidently it is important that the tolerances in the formation of the sleeve, and the opening in the hollow section, should be relatively close, so that the sleeve is a relatively tight sliding fit as it is introduced. This is necessary so that the surface formation on the sleeve head can make suitable gripping engagement with the wall of the opening in the metal section. This imposes a manufacturing cost, and also care and attention in the formation of the receiving holes in the hollow metal section. Evidently, if the sleeve is introduced into an over-sized opening, and the sleeve rotates freely in this opening while attempt is made to tighten the bolt, there will be idle rotation of the sleeve and the conical head and therefore no axial inward movement of the conical head.